1. Field of the Invention:
This invention relates to the rims of wheels for a two-wheeled vehicle.
2. Description of the Prior Art:
A two-wheeled vehicle, such as a bicycle or a motor bicycle, is usually provided with a braking system including a brake shoe which can be pressed against a wheel rim for stopping the rotation of a wheel by friction. Its braking performance largely depends on the coefficient of friction between the material from which the rim is formed, such as an aluminum alloy, and the rubber from which the brake shoe is formed. This coefficient of friction becomes lower if the rim or the brake shoe is wetted with rain, etc. As a result, the braking system fails to function satisfactorily.
Various attempts have been made to obtain, even if they are wet, an improved coefficient of friction which is close to the value which can be achieved when they are dry. They include (1) roughening the surface of the rim, (2) employing a brake show having a specially shaped sliding surface on which no film of water is formed, and (3) forming the brake shoe from an appropriately selected material which can be expected to give a satisfactorily high coefficient of friction even if it may be wet.
All of these attempts are, however, unacceptable. The method as stated at (1) above requires a machining job which needs a great deal of time and labor. Nevertheless, no effect can be expected to last for a long period of time, as the rim recovers a smooth surface in a relatively short time as a result of wear. The methods as stated at (2) and (3) are both supposed to employ a rim having a smooth surface. Therefore, a film of water is likely to be formed between the sliding surfaces of the rim and the brake shoe and cause a hydroplaning phenomenon.